The invention relates to backlight modules in flat panel displays, and more particularly, to the architecture of lamps and transformers in direct type backlight modules.
In direct type flat panel displays, lamps are directly placed at the bottom of the panel as the light source. FIG. 1a shows a conventional lamp module. The lamp module comprises an electric board 106, and a plurality of transformers 104 coupled to the electronic board 106 for alternating current (AC) power generation. The current flows through the lamps 102, the feedback circuit 108 and the electronic board 106 to form an electronic loop. FIG. 1b is a timing chart of an AC voltage, showing a sinusoidal wave having a frequency of 60 Hz. In this case, all lamps are soldered to a common node coupling to the electronic board 106 to form an electronic loop. The cost is significantly high.
FIG. 2a shows an improved lamp module. A first phase transformer 204 and a second phase transformer 208 are coupled to an electronic board 206, and two lamps 102 are cascaded therebetween. The AC voltages on the node V1 and V2 shown in FIG. 2b, comprise phases differing by 180 degrees to each other while the amplitude and frequency are identical. The electronic loop formed in such way reduces common node cost, however, each lamp requires one corresponding first phase transformer 204 or second phase transformer 208 to drive, and further cost reduction is still desirable.
FIG. 3 shows another improvement of the lamp module. A plurality of transformers 304 are coupled to the electronic board 306, each comprising node V1 and V2 applied by the AC voltages shown in FIG. 2b. Because each transformer 304 drives two lamps 102, the utilization rate is improved. In this case, the cost is reduced, however, the possibility of flashover is increased due to reduced space between positive and negative voltages. If the space therebetween is increased to avoid flashover, the size of transformers 304 grows exceedingly large, causing volume waste.